1. Field of the Invention
The present invention relates to a method for recovering indium by electrowinning and an apparatus therefor, and more particularly to a method for electrowinning of indium from an indium-containing hydrochloric acid solution after removing impurities by various chemical purification methods, and an apparatus therefor.
2. Description of the Art
Industrially, indium has been produced mainly by recovering indium from a byproduct in zinc smelting which contains a small amount of indium, for example, by recovering concentrated indium in a lead sulphate, and therefore a complex hydrometallurgical process has been required for isolating indium from impurities such as arsenic, zinc and cadmium. Generally, indium is recovered as a refined sponge indium by removing impurities to get a high indium content solution through various chemical purification methods in which an acid leaching, neutralization, an alkali leaching, sulphidizing and cementation are combined; and subjecting the high indium content solution to a cementation treatment by using a zinc plate or an aluminum plate. Then, the crude metal is cast to an anode, and electrorefining is carried out by using an indium starting sheet as a cathode and a sulfuric acid solution as an electrolyte so as to produce indium having a purity of 99.99% or more.
FIG. 3 shows a representative process for conventional indium purification.
After raw materials, for example crude metals, are dissolved in hydrochloric acid, H.sub.2 S gas is blown into for sulphidizing to precipitate Pb, Cd, Sn or Tl as sulfides. A purified Indium sponge is added to the solution after the sulphidizing to carry out a cementation for precipitating Sn. Further, a cementation with a zinc plate is carried out to precipitate Indium as a purified sponge. Thus obtained purified sponge is cast into an anode and then subjected to an electrorefining to produce an indium product.
The high indium content solution which is obtained through the above chemical purification method has a sufficiently lowered concentration of the impurities so that a high grade indium can be electrowon. However, the indium solution contains hydrochloric acid in order to dissolve the crude metal before the sulphidizing and also promote the isolation of the impurities in the sulphidizing treatment. Therefore, if the solution is directly subjected to an electrowinning, chlorine gas will disadvantageously be generated. In order to avoid generating chlorine gas, it has been required to recover indium first in the form of a refined sponge indium, cast it into an anode and then electrorefine it.